The class version can be flagged with V_PREVIEW (JEP 12)

asm-test/src/resources/java/jdk11/LambdaCondy.java

@@ -30,6 +30,8 @@ package jdk11;
 /**
  * By default with jdk 11, constant lambda are compiled using constant dynamic
  * The classfile was generated with the amber (branch condy-folding) compiler. 
+ * 
+ * /usr/jdk/jdk-11/bin/javac -source 11 --enable-preview jdk11/LambdaCondy.java
  */
 public class LambdaCondy {
   public static void main(String[] args) {

asm-util/src/test/resources/jdk11.LambdaCondy.txt

-// class version 55.0 (55)
+// class version 55.65535 (-65481)
 // access flags 0x21
 public class jdk11/LambdaCondy {
 
@@ -9,7 +9,7 @@ public class jdk11/LambdaCondy {
   // access flags 0x1
   public <init>()V
    L0
-    LINENUMBER 7 L0
+    LINENUMBER 36 L0
     ALOAD 0
     INVOKESPECIAL java/lang/Object.<init> ()V
     RETURN
@@ -19,15 +19,15 @@ public class jdk11/LambdaCondy {
   // access flags 0x9
   public static main([Ljava/lang/String;)V
    L0
-    LINENUMBER 9 L0
+    LINENUMBER 38 L0
     LDC run : Ljava/lang/Runnable; java/lang/invoke/LambdaMetafactory.metafactory(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/Class;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/Object; (6) [()V, jdk11/LambdaCondy.lambda$main$0()V (6), ()V]
     ASTORE 1
    L1
-    LINENUMBER 10 L1
+    LINENUMBER 39 L1
     ALOAD 1
     INVOKEINTERFACE java/lang/Runnable.run ()V (itf)
    L2
-    LINENUMBER 11 L2
+    LINENUMBER 40 L2
     RETURN
     MAXSTACK = 1
     MAXLOCALS = 2
@@ -35,7 +35,7 @@ public class jdk11/LambdaCondy {
   // access flags 0x100A
   private static synthetic lambda$main$0()V
    L0
-    LINENUMBER 9 L0
+    LINENUMBER 38 L0
     GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
     LDC "hello condy"
     INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V

asm/src/main/java/org/objectweb/asm/Opcodes.java

@@ -69,6 +69,14 @@ public interface Opcodes {
   int V10 = 0 << 16 | 54;
   int V11 = 0 << 16 | 55;
 
+  
+  /**
+   *  Version flag indicating that the class is using 'preview' features.
+   *  
+   *  {@code version & V_PREVIEW == V_PREVIEW} tests if a version is flagged with {@code V_PREVIEW}.
+   */
+  int V_PREVIEW = 0xFFFF0000;
+  
   // Access flags values, defined in
   // - https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.1-200-E.1
   // - https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.5-200-A.1

asm/src/test/java/org/objectweb/asm/ClassReaderTest.java

@@ -427,6 +427,20 @@ public class ClassReaderTest extends AsmTest implements Opcodes {
         0);
     assertTrue(success.get());
   }
+  
+  @Test
+  public void testPreviewMinorVersion() {
+    ClassReader classReader = new ClassReader(PrecompiledClass.JDK11_LAMBDA_CONDY.getBytes());
+    classReader.accept(
+        new ClassVisitor(Opcodes.ASM7_EXPERIMENTAL) {
+          @Override
+          public void visit(int version, int access, String name, String signature, String superName,
+              String[] interfaces) {
+            assertTrue((version & Opcodes.V_PREVIEW) == Opcodes.V_PREVIEW);
+          }
+        },
+        0);
+  }
 
   /** Tests that reading an invalid class throws an exception. */
   @ParameterizedTest

asm/src/test/java/org/objectweb/asm/ConstantsTest.java

@@ -67,6 +67,7 @@ public class ConstantsTest {
           assertFalse(asmVersions.contains(field.getInt(null)));
           asmVersions.add(field.getInt(null));
           break;
+        case "V_PREVIEW":
         case "V1_1":
         case "V1_2":
         case "V1_3":